We're now trying to book rooms in a couple of lodges in Australia for our trip. When contacting the lodge by email, they inevitably ask you to send them your credit card number. I'm very reluctant to provide my credit card number by email, as it's about the least secure way there is to transfer information over the net. So, I usually ask for a secure web-page to submit the number to (HTTPS pages use proven public key algorithms to transfer the data securely), and there's rarely a problem. But today I received two most original answers from two places. One says:

You can send the number in two different emails [...]

That is, if the card number is 1234 5678, send 1234 in one email, and 5678 in another. This is surely going to confuse them hackers :-D :-D
The other provided an even better algorithm:

If concerned about security you could use our fax number [...], or send your number via email and on the last set of four digits add 1 to each number for example, if your last 4 numbers on the card are 4566 send me 5677